Wedge cable clamps are used for cable strain relief in applications such as elevators to affix travelling control and power cables to a wall of an elevator shaft with an end of the cable connected to an elevator car. As shown in FIG. 1, a typical installation provides elevator shaft 10, in which elevator car 12 travels, with travelling control and power cable 14 in the form of a flat cable. Cable 14 runs along a wall 16 of elevator shaft 10 and connects to elevator car 12 by means of a bracket 18 affixed to the bottom of the car. A wedge cable clamp 20 is affixed to wall 16, typically at the mid-point of the elevator shaft, to secure the control and power cable to the wall 16.
In this example installation, one end of cable 14 is interconnected to elevator car 12 to provide the car with power and control signals to provide electric power to the car and control signals to allow for operation of the car. At the other end of the cable (not shown), cable 14 is connected to a power source and a control system for controlling the operation of the elevator car. Between the wedge clamp 20 and the bracket 18 on the elevator car 12, the control and power cable 14 is not fixed to wall 16 and is free to move away from the wall as elevator car 12 moves up the elevator shaft 10, eventually reaching the top of the shaft. As can be seen at the bottom of shaft 10, control and power cable 16 is provided a sufficient amount of slack 22 to allow for proper interconnection to bracket 18 when the elevator car 12 is at its lowest point (as shown). The amount of slack 22 also provides a sufficient amount of cable length for elevator car 12 to reach its highest point in elevator shaft 10 (not shown).
The wedge shaped clamp 20 may include a wedge shaped base portion 19 secured to wall 16 and a sliding portion 21, which is slideably mounted in the base portion. Cable 14 is placed in base portion 19 on a flat bottom surface and sliding portion 21 is inserted into guide rails on each side of the base portion. As the sliding portion 21 is moved within the base portion, a flat surface on the sliding portion, which opposes the flat surface of the base portion, comes into contact with the cable and applies pressure on the cable to secure it in place. During installation and removal of the cable, a hammer is typically used to apply force to the sliding portion 21 to secure it in place and then to loosen it to release the cable.
With the above-described type of clamp, the cable is held in place by the downward force of the wedge clamp applied to the cable and the wedge clamp is held in place due friction between the sliding portion 21 and the cable. Therefore, the sliding portion is susceptible to loosening over time. Moreover, the amount of force applied to the sliding portion 21 to hold it in place is not well controlled and can cause damage to the cable during installation if excessive pressure is applied.